I'm sorry for not getting the model # of this unit,but I hadn't planned to post this question.I was checking out a Goodman 2 ton a/c unit @ work today.It was 95+ degrees outside.My gauges read 83 lbs. on low side and around 275 on high side.The room temperature inside apartment was 79 degrees with a vent temperature of 66 degrees. My vapor line temp. should have been around 67 degrees,but was around 54 degrees. I figured it was over-charged and took out some freon. The line temp. went up momentarily,but went back down into the low 50's. This kept happening after taking out more freon a couple more times.I got frustrated and recovered all the freon from unit and metered the factory amount(6 lbs.) back in slowly. The line temp went down to 49 degrees with the low side pressure reading 90 lbs. and about 280 on high side.I checked filters and replaced them.The 2 return vents in apartment had good air-flow through them as did the a/c vents in unit.The ac unit right next to this one was working perfectly, so I'm at a loss for what to check now and would appreciate any input that is offered.

if you have a fixed type metering device, measure the suction line temperature (insulate the sensor). compare that number to the saturated suction temperature (temperature your gauge needle reads). what is the difference between the two ? this is superheat. an acceptable range could be anywhere from 7 to 20 degrees, depending upon other conditions.

if you have a txv type metering device, do the same thing with the liquid line - use the temperature number on the high side. this is subcooling. an acceptable range is typically 7 to 10 degrees.

you said you knew what the vapor line should be reading. should we assume from that there is a charging chart posted on the unit ? if this is the case, it is correct to use it. this overrides any other method. charging charts will require two readings in order to intersect for a third value. if there is not a chart, tell us the metering device type, the superheat and the subcooling.

also measure the return air and supply air. the difference between these two is commonly referred to as delta-t and should be (ideally) around 18. as mentioned, make sure airflow is good and coils are clean before further testing.